Diagnostic potential of simplified methods for measuring glomerular filtration rate to detect chronic kidney disease in dogs

BACKGROUND: Glomerular filtration rate (GFR) is the most sensitive indicator of initial renal function decline during chronic kidney disease (CKD), but conventional protocols for measuring GFR are labor‐intensive and stressful for the dog. OBJECTIVES: To assess the diagnostic potential for detecting CKD with simplified GFR protocols based on iohexol plasma clearance. ANIMALS: Seventeen CKD‐positive and 23 CKD‐negative dogs of different breeds and sex. METHODS: Prospective nonrandomized study. Plasma iohexol was measured 5, 15, 60, 90, and 180 minutes after injection. Glomerular filtration rate was calculated using 5 samples (GFR(5)) or simplified protocols based on 1, 2, or 3 samples. The GFR(5) and simplified GFR were compared by Bland‐Altmann and concordance correlation coefficient (CCC) analysis, and diagnostic accuracy for CKD by receiver operating characteristic curves. A gray zone for each protocol was bounded by the fourth quartile of the CKD‐positive population (lower cutoff) and the first quartile of the CKD‐negative population (upper cutoff). RESULTS: All simplified protocols gave reliable GFR measurements, comparable to reference GFR(5) (CCC >0.92). Simplified protocols which included the 180‐minutes sampling granted the best GFR measure (CCC: 0.98), with strong diagnostic potential for CKD (area under the receiver operating characteristic curve ± SE: 0.98 ± 0.01). A double cutoff including a zone of CKD uncertainty guaranteed reliable diagnosis outside the gray area and identified borderline dogs inside it. CONCLUSIONS: The simplified GFR protocols offer an accurate, hands‐on tool for CKD diagnosis in dogs. The gray zone might help decision‐making in the management of early kidney dysfunction.